The original goal was to study the contribution(s) of the neuropeptides substance P, neurotensin, and enkephalins (leu,met) to the regulation of secretion of anterior pituitary hormones. The specific aims were to examine the role of each peptide in the regulation of PRL or GH by micro- injecting substance P, neurotensin, or enkephalins into discrete regions of the hypothalamus and to study immunohistochemically at the light and electron microscopic levels the organization and synaptic relationships of peptidergic neurons in the hypothalamus. New directions were to determine whether the substance P content in the anterior pituitary is hormonally regulated. Progress includes: (1) findings suggesting that neurotensin microinjected in the medial preoptic area is associated with increased release of PRL, (2) the demonstration at the ultrastructural level that enkepha-linergic neurons in the paraventricular nucleus and somatostatinergic neurons in the anterior hypothalamus are involved in complex but specific synaptic relationships with several types of neuronal elements and have local axonal arborizations, (3) the observations by the Golgi method that four morphologically distinct projecting neurons, many of which collateralize locally, and two types of interneurons are present in the paraventricular nucleus, (4) the demonstration that substance P in the anterior pituitary is releasable and (5) the demonstration that both thyroid and gonadal hormones participate in the regulation of substance P in the anterior pituitary. The specific aims in the additional two years are extensions of the initial research activities: (1) to study the acute vs. chronic effects of microinjected neurotensin on they hypothalamic regulation of PRL secretion, (2) to study by immunohistochemistry the relationship of neurotensinor enkephalin-containing terminals to neurons in the paraventricular and medial preoptic regions that project to the median eminence, (3) to study the hormonal regulation of substance P in the anterior pituitary of the developing rat, (4) to study immunohistochemically the distribution of substance P containing cells and their relationship to other hormonal and peptide containing cells in the anterior pituitary in normal and hormonally-manipulated animals, (5) to study in vitro the direct effects of substance P on hormone release and interactions between substance P and factors known to regulate PRL, LH, and ACTH.